Hot roll supercalender



- June 24, 1969 Filed Mar ch 1. 1967 J. H. FREDRICKSON ETAL HOT ROLL SUPERCALENDER Sheet I ors INVENTORS JOHN H. FREDR/CKSON Q HARRY/1' KOHNE, JR.

GUNTHER K. HUNGER ATTORNEY Jfine 1969 J. H. FREDRICKSON ETAL 3,451,331

HOT ROLL SUPERCALENDER Sheet ,3 oliS Filed March 1, 196') INVENTORS JOHN H. FREDRICKSON HARRY E KOH/VE, JR. sun/mm K. HUNGER ATTORNEY J1me 1959 J. H. FREDRICKSON ETAL 3 L HOT ROLL SUPERCALENDER Sheet Filed March 1, 1967 INVENTORS JOHN/1'. FREDR/C/(SON HARRY]? KOHIVE, JR. GU/VTHERA. HUNGER ATTORNEY United States Patent 3,451,331 HOT ROLL SUPERCALENDER John H. Fredrickson, Glenwood, Gunther K. Hunger, Ellicott City, and Harry F. Kohne, Jr., Glenwood, MIL, assignors to Westvaco Corporation, New York, N.Y., a corporation of Delaware Filed Mar. 1, 1967, Ser. No. 619,653 Int. Cl. 1330b 3/04, 15/34; F28f 5/02 U.S. Cl. 10093 6 Claims ABSTRACT OF THE DISCLOSURE supercalender apparatus with alternating hard and soft rolls in a stack wherein the hard rolls are preferably of a thin-walled construction and at least one and up to three may be heated, the latter by independently controlled means to different temperatures and the soft rolls romprise the conventional cotton-filled type or may be fabricated from a synthetic material.

Brief summary of invention hydraulic, mechanical, or pneumatic system. The soft rolls provide a resilient surface in contact with the paper, and cause the calendering to be governed by rolling friction. As the soft rolls enter the nip during calendering, they are distorted so that their diameter is reduced, thus causing a slowing-up of the soft roll surface until a minimum is obtained at the center of the nip. As the soft rolls leave the center of the nip, they expand to their original size, and their surface speed increases, which produces a creep in the soft rolls in a direction opposite to the direction of rotation. This results in a polishing action on the paper next to the metal roll, since there is no appreciable displacement of the web relative to the soft roll because of the high coefficient of friction between the paper and the soft roll.

supercalendering produces a much higher finish than can be obtained on machine calenders. The gloss is higher because of the greater polishing effect. Gloss is obtained mainly by friction, whereas smoothness is produced main- 1y by pressure. Supercalenders produce not only a higher finish, but also a more uniform finish because of the resilient backing provided by the soft rolls.

The hard rolls used in the typical supercalender are metal, generally steel or chilled cast iron and the soft rolls are paper or cloth filled. The soft rolls may also be made from synthetics, such as nylon and Lexan.

When paper is put under the influence of supercalendering, many changes occur. These changes follow a definite pattern. Density and gloss increase very rapidly through the first two nips and the first 1000 pounds per linear inch pressure; but as further increases in pressure are made or more nips are employed, the rate of change becomes smaller. Bekk smoothness increases with pressure from zero to commercial pressures but increases at a steadily decreasing rate as the number of nips is increased. Print quality improved very rapidly with only one nip and pressures up to 1000 pounds per linear inch.

The opacity and brightness generally drop with super- "ice calendering; however, this loss is not significant until commercial pressures are reached. Moistening during the supercalender operation as a means of improving print quality, gloss, and smoothness does not provide any significant gains at application levels of less than 5%. At higher application levels, an additional 50% increase in gloss may be obtained, but opacity and brightness suffer severe losses.

The hereinbefore characteristics of a typical supercalender and the effects of supercalendering paper apply both to coated and uncoated paper. However, the instant invention was arrived at as a result of investigations carried on in research to develop a coated paper with a density and continuity such that the paper would display an unusually high varnish holdout and gloss. Since most coated paper is supercalendered, it was our objective to investigate the possible variations which could be applied during the supercalendering step in the manufacture of coated paper to produce a commercially superior product.

Coated paper will blacken when supercalendered if the moisture content is too high. This phenomena results in a severe loss of brightness at highly compressed spots and loss of light refraction from the densified pigment surfaces. An important single property in supercalendering coated paper is the moisture content of the coating. Other factors which are important in the outcome of supercalendering coated paper include the type of pigment, type of adhesive, adhesive-to-pigment ratio, and the presence of waxes and other ingredients.

Realizing the effects and variables present in the step of supercalendering coated paper, we observed the results of previous attempts by others to produce paper which would accomplish our requirements. Invariably, these prior attempts had been centered around increasing supercalender loadings and changes in coating formulations. These experiments resulted in blackening or crushing of the sheet and failed to produce adequate varnish holdout. Earlier work by our company had shown high gloss and smoothness could be obtained by applying water to the coated paper surface prior to supercalendering. As a result of these endeavors we decided to make investigations concentrating on a variation in moisture content of the paper, running in the supercalender at lower loadings but with the addition of heated metal rollls. As a result of these studies we found that coated paper taken from the paper machine with a moisture content of around 7% could be supercalendered in a supercalendar having from one to three heated rolls at substantially reduced calendar loadings to give a glazed, impervious surface to the coating yielding good gloss and unusually good varnish holdout. This arrangement further reduced the crushing and blackening of the paper as a result of the lower pressure, surface concentrated mechanism. Further studies showed that optimum results were obtainable when more than one metal roll wase heated, and, the heat to each of the respective rolls was independently controlled at different temperatures. This invention, then, produced a commercially acceptable paper suitable for labels or other markets where varnish holdout would be a necessary property.

For our early experiments, a hollow steel roll with a thin 2 /2 inch thickness shell was installed on our experimental supercalender. The roll was heated by introducing p.s.i.g. steam into the roll through hollow journals and condensate was removed by means of an appropriate syphon system. A thin walled steel roll was used in order to achieve a quicker heat-up and cool-down time and also to maintain a more uniform temperature distribution across the roll face, so as to prevent heat distortion. Special attention was paid to the method of initiating operation of the supercalender with respect to threading of the paper and run-up particularly when synthetic soft rolls were employed in the supercalender stack. It was found that lifting devices were necessary to separate the heated roll, or, rolls from the soft rolls during heat up in order to prevent damage to the soft roll cover. Other problems with threading the supercalender prior to a run and after a break were encountered, but these difliculties have been substantially overcome so that our present production apparatus is capable of producing the superior product as set out hereinbefore.

Description of the drawing FIGURE 1 shows a schematic view of a typical supercalender stack incorporating the features of our invention;

FIGURE 2 shows schematically the preferred steam heating system for heating the metal rolls;

FIGURE 3 shows a detailed view partly in section of the preferred steam joint;

FIGURE 4 shows a partial view in section of the left end of the thin-walled metal roll construction used in our invention; and

FIGURE 4A shows the right end of the metal roll of FIGURE 4.

Detailed description FIGURE 1 shows a schematic representation of the supercalender stack of our invention which is presently being used in production. The paper Web W is mounted in reel form on an unwind stand so that the web W can be directed around guide rollers 14, 16 to the stack. The web W then passes through the stack comprising hard, metal rolls 18, 20, 22, 24 and 26 and soft rolls 28, 30, 32, and 34. Conventional fly rolls 27, 31 are used on each side of the stack to guide the paper web W through the nip. From the stack the paper web W continues around guide rollers 36, 38 to the rewind stand 12. As will be noted in FIGURE 1, the three intermediate metal rolls 20, 22, 24 are each indicated as being heated but are not all necessarily heated at the same time. We found after experimentation that the paper should be fairly moist with up to about 7% moisture, when coming to the supercalender stack, and, that it was better to exchange some pressure on the supercalender for heat. The best results were obtained at pressures below 1600 pounds per linear inch, preferably, in the neighborhood of between 1550 and 1650 pounds per linear inch, increasing the heat according to the desired finish of the paper. Our supercalender design using the thin shell metal roll as shown in FIG- URE 4, allows the hot roller rolls to be heated up quickly. After the roll or rolls reach the resired temperature, and paper begins to pass through the stack, an equilibrium running temperature is achieved in approximately three minutes. When more than one hard roll is heated, they are each preferably heated at different temperatures between 180 to 325 degrees Fahrenheit, according to the steam pressure being used. As a result of these variations it was found that optimum results were obtainable by running each of the rolls at a lower heat than by running one roll extremely hot. Since the supercalendering operation is a dynamic process, the operating temperatures and pressures are always fluctuating. Actual mill production runs show that the soft roll becomes quite warm during operation. At the beginning of a typical running period using one heated roll, the hard roll is brought up to an initial temperature of about 240 degrees with the soft roll at 100 degrees. After the run starts, an equilibrium temperature is reached with the hard rolls operating at about 210 degrees and the adjacent soft roll at 140 degrees.

FIGURE 2 shows schematically our steam application system for heating one or more of the intermediate metal rolls. The steam introduced through line 40 at 180 p.s.i.g. and 379 F., to a shutoff valve 42 into distribution line 46. The distribution line 46 leads to the metal rolls 20,

22, 24 by way of a rotary joint means 60, controlled by valve 48. A temperature gage 5t) and pressure gage 52 is connected into the line at each side of the metal roll so that the steam conditions may be controlled and monitored. In actual practice, these temperatures and pressures are monitored at a control station by the supercalender operator. The rotary joint 65) chosen for our application is desirably a Barco type CC joint, one inch in diameter as shown in FIGURE 3. This particular steam joint was selected after a series of experiments showed it to function the best with minimum maintenance and apparent longevity. FIGURE 3 shows the flexible hose coupling 62 which requires special attention during assembly of the system. Experience demonstrated that the coupling 62 could not be loaded during operation, or the seal would fracture. Therefore, a flexible metal hose was used bent at an angle to absorb any movement due to expansion and contraction under pressure and temperature changes.

The hose coupling is secured by torque restrainer 64 to an elbow 66 and then to the inner steam conduit 76. The entire steam joint including seal 70 and bearings 74 is urged by spring means 72 against the retaining ring 78 which is attached to the roll by cap screws 68. The seals 70 and bearings 74 are replaceable in the joints by removing the retaining ring 78 from the rear of the housing. All of the parts then slip out of the housing. This particular steam joint, the Barco type CC rotary joint has been tested for 250 p.s.i.g. and 400 F. at speeds in excess of 480 rpm.

FIGURE 4 shows in detail the preferred construction of our thin-walled heated metal roll The Barco type CC Rotary steamjoint is shown on the right side of FIGURE 4 attached to the end of roll 80. The roll itself is fabricated in three parts, including two outside parts 82 mounted in the respective bearing housings 81 intermediate roller bearings 83, and, the innermost part 84. The roll element 84 comprises a bored, thin-walled calender roll having approximately a 2 /2 to 3 inch wall thickness. The innermost part 84 is fixedly attached to the outside parts 82 by cap screws 87. Bearing housings 81 each include the conventional oil seals, bearing lock washers and locknuts.

After continued experimentation, the syphon system finally chosen to remove condensate from the heated roll was of the rotating syphon design. This system proved best for a high, dryer steam pressure with a good condensation rate. FIGURE 4 shows a syphon pipe 86 extending inside the innermost part of the calender roll 84 which collects the condensate and conducts it to line 54 (FIGURE 2) where it is either vented to the atmosphere, or, depending on the setting of valve 55, conducts the condensate back to the condensate return system including steam trap 58 and drain valve 56. The syphon tube 86 extends through a Teflon tube 89 mounted in outer roll part 82. The left side of the roll of FIGURE 4 then includes a rotary union adapter attached to the roll element 82, a rotary union cartridge assembly 92 and a special syphon elbow 94. Basically the rotary syphon system of our invention introduces steam at one side of the roll and removes condensate from the other side. This system was found to be superior and required less maintenance than a dual syphon system.

In the preferred embodiment of our invention, the heating system employed for the metal rolls is steam as hereinbefore set out. FIGURE 2 shows a control valve 48, temperature gage 50 and pressure gage 52 in the steam line both before and after the steam enters the roll. These valves and gages are used to differentially control the heat in each roll and monitor the performance of the system. Of course, it is within the scope of our invention to employ other different forms of heating means, such as gas firing, electrical resistance heating and circulating oils, and, the differential control and monitoring system would necessarily be changed accordingly.

As hereinbefore stated, the soft roll construction capable of use in our invention varies from the ordinary paper or cloth filled rolls to rolls covered with a synthetic material. Experimentation .with Lexan in particular illustrated that a long roll life could be expected in the hot supercalender. Lexan is a polycarbonate marketed by General Electric Company. The manner in which the Lexan roll cover is fabricated is not a subject of this invention, and any well known means may be employed.

Lexan, with a chemical structure substantially as follows:

has proven to be superior to other synthetic materials because it has a good coeificient of thermal expansion, shows low internal friction, is not brittle and has a reasonable modulus of elasticity. Each of these attributes are necessary in a soft roll, especially when running against a heated metal roll in a Supercalender apparatus.

If it were desirable to give the supercalendered paper a double finish, it is further within the scope of our invention to place two soft rolls adjacent one another in the stack.

While We have herein shown and described one form in which our invention could be embodied, it may readily be understood that various modifications in the invention may be attained without departing from the spirit and scope of the novel concepts thereof.

We claim:

1. Supercalender apparatus comprising:

(a) a vertically aligned stack of alternate hard and soft rolls mounted for rotational movement in a frame;

(b) means for feeding paper to be supercalendered into said stack;

(c) means for withdrawing and rewinding the paper after passing through said stack;

(d) means for applying pressure to said stack;

(e) means for driving at least one of said rolls;

(f) said stack having three or more hard rolls;

(g) one of said hard rolls being constructed from three individual pieces including;

( 1) a thin-shelled hollowed out central portion having a wall thickness not to exceed three inches; and,

(2) a pair of journals attached to the ends of said hollowed out central portion mounted in bearing housings in said frame; and,

(h) means for heating said thin-shell hard roll to a surface equilibrium temperature of approximately 210 degrees Fahrenheit.

2. The apparatus of claim 1 wherein said means for heating the thin-shelled hard roll comprises:

(i) a rotary steam joint connected to one end of said hard roll for conducting high pressure steam into said hollowed out central portion; and

(j) a rotating syphon system connected to the opposite end of said hard roll for removing condensate from said hollowed out central portion. 3. The apparatus recited in claim 2 further characterized in that at least one of the soft rolls adjacent said 5 heated hard roll is covered with a synthetic material.

4. The apparatus recited in claim 3 further characterized in that said synthetic material comprises a polyaryl carbonate having the structural formula:

5. Supercalender apparatus comprising:

(a) a vertically aligned stack of alternate hard and soft rolls mounted for rotational movement in a frame;

(b) means for feeding paper to be supercalendered into said stack;

() means for withdrawing and rewinding the paper after passing through said stack;

(11) means for applying pressure to said stack;

(e) means for driving at least one of said rolls;

(f) said stack having three or more hard rolls;

(g) each of said hard rolls being constructed from three individual pieces including;

(1) a thin-shelled hollowed out central portion having a wall thickness not to exceed three inches, and,

(2) a pair of journals attached to the ends of said hollowed out central portion mounted in said frame; and

(h) means for independently heating said thin-shelled hard rolls to diiferent temperatures between the range of 180 to 325 degrees Fahrenheit.

6. The apparatus of claim 5 wherein said means for heating the thin-shelled hard rolls comprise:

(i) a rotary steam joint connected to one end of each of said hard rolls for conducting high pressure steam into said hollowed out central portions; and

(j) a rotating syphon system connected to the opposite end of each of said hard rolls for removing condensate from said hollowed out central portions.

References Cited UNITED STATES PATENTS 1,714,261 5/1929 Eganetal. 1,739,572 12/1929 Bidwell 1o0-93 2,436,530 2/1943 Sando 165-89 2,599,346 6/1952 Olfen 165-89 2,367,414 1/1959 Maloney 61231. 100-93 X 3,091,173 5/1963 KOCh 100-162 3,190,212 6/1965 MOOIC 100-93 X 3,230,367 1/1966 Nelson 10o- 93 3,336,362 8/1967 Brundige etal 100-162 3,364,343 1/1963 Muller 100-163 X PETER FELDMAN, Primary Examiner.

U.S. Cl. X.R. -162; -89 

